The use of conductivity measurements to analyze various characteristics of specimens such as human tissue specimens and geological specimens has been shown to yield many practical advantages. For example, conductivity measurements have been used to distinguish diseased tissue from healthy tissue. Both conventional electrode and induction coil methods have been used to perform conductivity measurements of various specimens.
Conventional electrodes for measuring conductivity apply an AC voltage to a specimen of interest. The current traveling through the specimen is measured and the conductivity is computed. In some cases, many electrodes are attached so that imaging of the specimen is made possible in circumstances where conductivity varies spatially through the specimen.
A disadvantage of conventional electrodes is that it requires direct electrical contact with the specimen of interest. This is particularly true for specimens having a surface that impedes the flow of current through the specimen. For example, the stratum corneum layer of the epidermis may impede the flow of current through a human tissue specimen, leading to variable conductivity measurements. Conventional electrodes may also exhibit electrode polarization, resulting in inaccurate conductivity measurements.
Induction coil methods and devices for measuring conductivity have used a wide variety of induction coil designs including solenoids or simple loop type coils consisting of a few turns of wire. These coils may probe the specimen at depths allowing interferences from portions of the specimen that distort the conductivity measurement. Many of these devices also involve the use of expensive instrumentation to measure coil related parameters such as complex impedance and use circuitry that permits the induction coil to deviate from resonance as the coil is placed adjacent to a specimen, making measurement of conductivity more difficult.
Therefore, a need currently exists for an induction coil conductivity sensor that overcomes these deficiencies. An induction coil conductivity sensor that probes a specimen at sufficient depths while avoiding unnecessary interferences from the specimen would be particularly beneficial. Additionally, an induction coil conductivity sensor that drives the sensor circuitry to resonance when the induction coil is placed adjacent to the specimen would also be particularly beneficial.